Ants use herbicide on their gardens

A type of Amazonian ant landscapes its own “garden” by using its own herbicide to kill plants.

Ants were farming long before humans. Previous studies have shown that leaf-cutter ants make compost in their nests to grow an edible fungus, while other types of ants keep “herds” of aphids in order to harvest their secretions of nutritious plant juices.

But Megan Frederickson and her colleagues at Stanford University, US, wanted to know whether the ant Myrmelachista schumanni could be responsible for cultivating large clumps of trees in the Amazonian rainforest that are made up almost entirely of one species, Duroia hirsuta, which, according to local legend, are cultivated by an evil forest spirit. They are also where the ant likes to live.

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To see whether these devil’s gardens, as they are known locally, are the ants’ handiwork or the result of competition between tree species, Frederickson planted saplings of a common Amazonian cedar either inside or outside the gardens, protecting some saplings from the ants and some not.

Within five days worker ants had devastated the unprotected saplings in the garden, by poisoning them with formic acid, causing most of the leaves to drop off.

This behaviour could allow more D. hirsuta trees to grow in the area cleared by the ants, enabling the colony to massively expand its number of nest sites, says Frederickson. This may explain how some colonies are able to survive as long as 800 years.